Conventional screens are divided into transmission-type screens and reflection-type screens. As shown in FIG. 1, a conventional transmission-type screen comprises a front transparent surface, and a rear scattering surface made of a thin film. As shown in FIG. 2, a conventional Fresnel transmission-type screen comprises a Fresnel lens installed at a front surface, and a real vertical curved surface, thereby transmitting light through the front surface serving as an incidence plane (D) and diffusing an image through the rear surface serving as an exit plane (E). Thus, the Fresnel transmission-type screen displays the image through the exit plane (E). However, since light is incident on the incidence plane (D) of the Fresnel transmission-type screen, it is impossible to display the image through both surfaces, i.e., front and rear surfaces of the screen.
Further, since the above-described conventional screens have a sheet structure made of a hard material, it is difficult to roll the screens or to transfer and/or store the screens.
Accordingly, in order to allow the conventional screens to display an image through both surfaces thereof, the screen requires two sub-screens, i.e., front and rear screens, and two projectors, i.e., front and rear projectors.
Moreover, as shown in FIG. 3, in case that the conventional transmission-type screen 8 is has a high transmittance in order to increase the brightness of the transmission-type screen 8, a beam of light projected from a projector 5 located adjacent to a rear surface of the transmission-type screen 8 is transmitted through the transmission-type screen 8 and is then exposed to the outside, thus generating a hot spot (F), such that an area around a light source lamp 7 through a projection lens 6 is more brighter than other peripheral areas. The above hot spot (F) is generated also in a reflection-type screen. The generation of the hot spot (F) is proportional to the reflectance of the screen. Thus, in case that the screen has a higher reflectance, the hot spot (F) has an increased size throughout the screen, thereby deteriorating the uniformity of the brightness of an image formed on the screen. Accordingly, there has been required a technique for eliminating the generation of the hot spot (F).
More specifically, in the transmission-type screen 8 as shown in FIG. 3, the projection lens 6 of the projector 5 located adjacent to the rear surface of the transmission-type screen 8 faces the transmission-type screen 8. Here, a light source of the light source lamp 7 within the projection lens 6 of the projector 6 is viewed through the projection lens 6, and the light source is projected onto the transmission-type screen 8. Thus, viewers view both the light source of the light source lamp 7 and an image formed the transmission-type screen 8. That is, there is generated the hot spot (F) such that a central area of the screen is brighter than other peripheral areas of the screen. Thereby, the brightness of the screen 8 is not uniform.
Since viewers view the light source of the light source lamp 7 by reflection of a reflection-type screen, such a hot spot (F) is generated also in the reflection-type screen.